Cancer is a major disease that continues as one of the leading causes of death at any age. In the United States alone, it is estimated that more than a half a million Americans will die annually of cancer. Currently, radiotherapy and chemotherapy are two important methods used in the treatment of cancer.
Considerable efforts are underway to develop new chemotherapeutic agents for more potent and specific anti-cancer therapy, presenting effective and efficient cytotoxicity against tumor cells, with minimal interference with normal cell function. Accordingly, there is an urgent need for the development and analysis of novel, effective anti-cancer agents.
Cellular proliferation, for example, in cancer, occurs as a result of cell division, or mitosis. Microtubules play a pivotal role in mitotic spindle assembly and cell division. These cytoskeletal elements are formed by the self-association of the αβ tubulin heterodimers.
Recently, the structure of the αβ tubulin dimer was resolved by electron crystallography of zinc-induced tubulin sheets. According to the reported atomic model, each 46×40×65 Å tubulin monomer is made up of a 205 amino acid N-terminal GTP/GDP binding domain with a Rossman fold topology typical for nucleotide-binding proteins, a 180 amino acid intermediate domain comprised of a mixed β sheet and five helices which contain the taxol binding site, and a predominantly helical C-terminal domain implicated in binding of microtubule-associated protein (MAP) and motor proteins.
As disclosed in U.S. Pat. No. 6,258,841 B1, tubulin has a binding pocket in a region within the intermediate domain of tubulin, located between the GDP/GTP binding site and the taxol binding site. The approximate dimensions of the binding pocket are 6 Å×22 Å×7 Å. The pocket, referred to as the COBRA binding pocket, has an abundance of leucine residues (7 leucine and 2 isoleucine) providing a highly hydrophobic binding environment. It is characterized by a narrow cavity with elongated dimensions, suitable for accommodating an aliphatic chain of up to about 12 carbons.
Compounds that bind with the COBRA binding pocket can interfere with tubulin polymerization and can provide novel agents for the treatment of cancer.